In the field of the graphic arts, to improve the reproduction of images having a continuous gradation of dot images or the reproduction of line images, an image forming system is needed which provides images having high contrast (gamma: not less than 10).
For this purpose, a special developer called a lith developer has been used. The lith developer contains only hydroquinone as a developing agent and the concentration of free sulfurous acid ions in the lith developer is greatly decreased by using sulfites as a preservative in the form of an adduct with formaldehyde so that they do not inhibit infectious developing properties. The lith developer is readily subject to air oxidation. The fact that it cannot be stored for more than 3 days is a serious disadvantage.
As a method for obtaining photographic characteristics of super high contrast using a stable developer, a method using hydrazine derivatives, as described in, for example, U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,221,857 and 4,243,739, is known. In accordance with this method, photographic characteristics of high contrast and high sensitivity can be obtained and since a high concentration of sulfite can be added to the developer, the stability of the developer against air oxidation is greatly increased in comparison with the lith developer.
However, in order to obtain photographic characteristics of high contrast and high sensitivity, a relatively long developing time is needed. For example, in the examples of the above U.S. Patents, a developing time ranging between 1 minute and 3 minutes is usually employed. There is tendency that as the pH value of the developer decreases, a longer developing time is needed.
In the field of graphic arts, stabilization of the developer and acceleration of processing have been strongly desired in recent years. Thus it is very important to solve the above problem.
Among the methods to directly obtain positive images by the color diffusion transfer method is a method using a combination of internal latent image type emulsion and hydrazine derivatives.
This combination, however, fails to provide negative images of high contrast to the extent that the present invention is intended to provide.
U.S. Pat. No. 3,846,129 discloses a color diffusion transfer method using a combination of hydrazine derivatives as described above and internal latent image type emulsions in which an aromatic alcohol dye booster is added to a para-phenylenediamine-type viscous developer along with a competing developer.
In this method, however, aromatic alcohols are considered to act as agents which accelerate the transfer of formed dyes. The mutual action of the aromatic alcohols with hydrazine derivatives is not at all suggested.
A method is known in which aromatic alcohols, specifically those described in Japanese Patent Application (OPI) No. 200250/85 (the term "OPI" as used herein means a "published unexamined Japanese patent application") are added to a developer to be used in the system using hydrazine derivatives. In fact, however, the solubility of the aromatic alcohols is, however, not sufficiently high to dissolve more than a small amount. Thus they are used in only a small amount within the concentration range in which they can be dissolved.